Extension means of a multi-stage boom

ABSTRACT

A multi-stage boom having at least three telescopic sections extendible and retractable relative to one another. A first cylinder means coacts between first and second boom sections for permitting relative movement therebetween, and a second cylinder means coacts between second and third boom sections for permitting relative movement therebetween. A fluid pressure control system is connected to the cylinder means for permitting the boom sections to be sequentially automatically extended or retracted. The control system includes a switching valve which, during extension of the boom, initially supplies pressure fluid to the first cylinder means to cause extension of the second boom section. The switching valve is automatically shifted when the second boom section is fully extended to cause pressure fluid to be supplied to the second cylinder means for causing the third boom section to be automatically extended relative to the second boom section. The shifting valve functions in the reverse manner upon retraction of the boom for causing the sections thereof to automatically but sequentially retract.

United States Patent Yunoki et al.

[54] EXTENSION MEANS OF A MULTI- STAGE BOOM [72] Inventors: Tadao Yunoki; Toshio Fujiyasu, both of Oh-Machi, Japan Kabushiki Kaisha Tadano Tekkosho, Shinden-cho, Takamatsu, Kagawa Prefecture,

Japan V v 1 v.

22 Filed: March 16, 1970 21 Appl.No.: 19,717

[73] Assignee:

[30] Foreign Application Priority Data March 20, 1969 Japan ..44/21406 March 17, 1969 Japan ..44/20283 [52] U.S.Cl.. ...91/168,9l/l89 [451 June 27, 1972 3,301,136 l/1967 Bolton et al. ..91/189 Primary Examiner-Paul E. Maslousky Attorney-Woodhams, Blanchard and Flynn [57] ABSTRACT A multi-stage boom having at least three telescopic sections extendible and retractable relative to one another. A first cylinder means coacts between first and second boom sections for permitting relative movement therebetween, and a second cylinder means coacts between second and third boom sections for permitting relative movement therebetween. A fluid pressure control system is connected to the cylinder means for permitting the boom sections to be sequentially automatically extended or retracted. The control system includes a switching valve which, during extension of the boom, initially supplies pressure fluid to the first cylinder means to cause extension of the second boom section. The switching valve is automatically shifted when the second boom section is fully extended to cause pressure fluid to be supplied to the second cylinder means for causing the third boom section to be automatically extended relative to the second boom section. The shifting valve functions in the reverse manner upon retraction of the boom for causing the sections thereof to automatically but sequentially retract.

10 Claims, 9 Drawing Figures PATENTEDJm'r 1972 3. 672.257

sum 50F 5 Fig. .9

' INVENTORS TAD/l0 YUA/OK/ Tos/l/o fuf/msu ATTO EYE EXTENSION MEANS OF A MULTI-STAGE BOOM The present invention relates to an extension means of a boom consisting of at least three boom members telescopically extensibly connected to each other.

The most commonly used extension means of a boom consisting of at least three extensible boom members is so constructed that hydraulic cylinders are respectively disposed between adjacent two boom members, and oil supply lines are are connected to the respective hydraulic cylinders so as to cause these boom members to extend and retract. The conventional and existing arrangements of the oil pressure supply lines or circuits in the type of extension means of the multistage boom are various: one of them is such that oil pressure supply circuits are respectively arranged at respective hydraulic cylinders of respective boom members, and a valve is connected to each of the oil pressure supply lines, thereby to independently control the extending and retracting motions of respective boom members; and the other practice is such that a pair of oil pressure supply and discharge lines or circuits are arranged for respectively connecting the compressed oil chamber on the extending side and the compressed oil chamber on the retracting side of each hydraulic cylinder arranged between boom members and a valve is connected therebetween for switching the hydraulic pressure; In the latter case, as a means for regulating the operational sequence of respective boom members, various mechanism have been used in combination for connecting adjacent boom members, such as cables so as to operate each of them in regular sequence; or disposing between adjacent boom members any suitable securing means automatically engaging or disengaging in association with the extending motion of each boom; or making a dimensional difference of a piston rod on which the working pressure is to be exerted in the direction of extension or retraction of pistons of respective hydraulic cylinders.

These conventional boom extension means as described, however, respectively present many disadvantages and inconveniences in structure and operation: for example; to dispose a valve for switching the hydraulic pressure at every hydraulic cylinder connected between boom members is not only difficult in piping work but also inconvenient in operating each valve; to use cables or securing means for controlling the operational sequence of respective boom members increases the complexity in structure of relevent portions; and to control the operational sequence of boom members by making a dimensional difference in the pressure exerted areas on respective piston rods results in unnecessary enlargement of a boom, because, with increment in the numbers of boom member, the working pressure exerted area on the piston rod of the preceding hydraulic cylinder, of which the diameter is smaller than that of succeeding cylinder must be larger than that on the piston rod of the succeeding hydraulic cylinder having the diameter larger than the preceding cylinder. This requirement is satisfied by imparting the sufficient strength to the preceding cylinder. However, this inevitably results in unnecessary increase in size and strength of the succeeding hydraulic cylinders.

The present invention overcomes these drawbacks as described.

Accordingly, an object of the present invention is to provide an extension means of a boom wherein the oil pressure is supplied to and discharged from respective hydraulic cylinders through oil pressure supply and discharge lines to which a valve for switching the oil pressure is connected, and extending and retracting motions of respective hydraulic cylinders for operating respective boom members are automatically controlled in relation with the extending or retracting motion of adjacent hydraulic cylinders.

Another object of the present invention is to provide an extension means of a boom wherein respective boom members are extended and retracted in regular sequence by the simple operation.

The present invention primarily comprises an extension means for a boom having an oil pressure supply and discharge line selectively connectable to an oil pressure supply source, oil pressure supply and discharge lines each connected to each of hydraulic cylinders, and at least a switching valve connected between the firstly mentioned oil pressure supply and discharge line and one of the secondly mentioned oil pressure supply and discharge lines which is connected to a hydraulic cylinder of a preceding position with respect to said switching valve, said switching valve having means automatically biased to positions for communicating said firstly mentioned oil pressure supply and discharge line with one of said secondly mentioned oil pressure supply and discharge lines in association with extending and retracting motions of adjacent hydraulic cylinders.-

The subject matter of the present invention consists in an extension means of a multi-stage boom which comprises a switching valve connected between an oil pressure supply and discharge line selectively connected to a pressure source and each of oil pressure supply and discharge lines connected to compressed oil chambers on the extending sides of hydraulic cylinders located at a preceding position with respect to said switching valve, said secondly mentioned oil pressure supply and discharge lines being selectively connected to said firstly mentioned oil pressure supply and discharge line according to a predetermined sequence, said switching valve having means automatically biased to a position for communicating said firstly mentioned oil pressure supply and discharge line with said secondly mentioned oil pressure supply and discharge line connected to the hydraulic cylinder of the preceding position with respect to said switching valve when the hydraulic cylinder of the succeeding position thereof reaches the utmostly retracted position, and further biased to a position for communicating said firstly mentioned oil pressure supply and discharge line with said secondly mentioned oil pressure supply and discharge line connected to the hydraulic cylinder of the succeeding position with respect to said firstly mentioned switching valve when the hydraulic cylinder of the preceding position with respect to said firstly mentioned switching valve reaches the utmostly extended position.

In the accompanying drawings showing examples of an extension means of a boom according to the present invention;

FIG. 1 is an illustrative view of one example of the extension means of a boom consisting of three boom members;

FIG. 2 is a diagrammatical view showing an arrangement of oil pressure supply and discharge lines connecting respective hydraulic cylinders;

FIG. 3 is an illustration showing a relation between an automatic switching valve and boom members, in which the automatic switching valve is shown in section;

FIG. 4 is a diagrammatical view of an arrangement of oil pressure supply and discharge lines in which the extension means is used in a boom consisting of four boom members;

FIG. 5 is an illustration of the other example of the extension means of a boom consisting of three boom members;

FIG. 6 is a diagrammatical view showing an arrangement of oil pressure supply and discharge lines connecting respective hydraulic cylinders;

FIG. 7 is a view showing a valve for automatically switching the oil pressure similar to FIG. 3 and its connection with respecu've oil pressure supply and discharge lines; and

FIGS. 8 and 9 are arrangements of oil pressure supply and discharge lines in which the extension means is used in a boom consisting of four boom members.

Description will be made with reference to the accompanying drawings.

In FIGS. 1 through 4, numerals l, 2 and 3 are first, second and third boom members telescopically slidably connected to each other and having a cylindrical shape. Numeral 11 is a hydraulic cylinder invertedly disposed between the first and second boom members to extend in a longitudinal direction of the boom, said hydraulic cylinder having a piston rod 11b which at its end is pivotally connected at 21 to the base portion of the first boom member 1 and a cylinder portion 11a which at its base portion is pivotally connected at to the base portion of the second boom member 2 located in the succeeding position with respect to the first boom member 1. Numeral 12 is a second hydraulic cylinder invertedly disposed between the second and third boom members 2, 3 to extend in the longitudinal direction, similar to the first hydraulic cylinder 11, said second hydraulic cylinder 12 having a piston rod 12b pivotally connected at 23 at its one end to the base portion of the second boom member 2 of the succeeding position with respect to the first hydraulic cylinder and a cylinder portion 12a pivotally connected at 24 at its top end portion to the top end portion of the third boom member 3 of the mostly succeeding position. Numeral 25 is a roller carrying the top end portion of the first hydraulic cylinder 1 1.

An arrangement of oil pressure supply and discharge lines connecting the first and second hydraulic cylinders l 1, 12 is as follows. Numeral 26 is a manual control valve for switching the oil pressure, 27 is an oil pressure and discharge line or circuit being communicated with the compressed oil chamber 11d on the retracting side of the first hydraulic cylinder 11 through a port 28 provided at the piston rod 11b of the first hydraulic cylinder 11 and an oil passage lle provided at said piston rod 11b. Said compressed oil chamber 11d is communicated with the compressed oil chamber 12d on the retracting side of the second hydraulic cylinder 12 through a port 29 provided at the cylinder portion 11a, an oil pressure supply and discharge line 30, a port 31 provided at the piston rod 12b of the second hydraulic cylinder 12 and an oil passage 12c provided at said piston rod 12b. The supply and discharge of oil pressure to and from the compressed oil chambers 11c, 12c on the extending sides of respective hydraulic cylinders 11, 12 are effected through a common oil pressure supply and discharge line 32 connected between said valve 26 and a switching valve 33. The respective compressed oil chambers llc, 12c on the extending sides of hydraulic cylinders 11, 12 and said switching valve 33 are connected through the oil pressure supply and discharge lines 34, 35, respectively. Numeral 36 is a port connecting the oil pressure supply and discharge line 34 to the compressed oil chamber 11c on the extending side of the first hydraulic cylinder 11, and 37 is a port provided at the piston rod 12b for connecting the oil pressure supply and discharge line 35 to the compressed oil chamber 12c on the extending side of the hydraulic cylinder 12. Said switching valve 33 is mounted on the second boom member 2. The oil pressure supply and discharge line 32 connected to said valve 33 is so designed that the mid portion thereof is extensible by any suitable means; for example, a flexible hose 32' extensible by a winding pulley 38 is inserted. The construction andv operation of the switching valve 33 which is automatically switched according to the extending and retracting motions of respective boom members 2, 3 will be described hereunder.

In FIG. 3, the valve 33 for switching the oil pressure includes a valve body 39 secured to the base portion of the second boom member 2, a plunger 40 provided with an annular oil passage 41, a port 42 communicating with the oil pressure supply and discharge line 32, a port 43 to which the oil pressure supply and discharge line 34 is connected, a port 44 to which the oil pressure supply and discharge line 35 is connected, and a sliding metallic actuator element 46 slidable in the direction of a-a' within a slot 46' formed in the body 39. Said plunger 40 is normally pressed in the a direction by a spring 45. Said sliding metallic element 46 is provided with a roller 47 on its top portion, which faces a projection 48 provided at the inner periphery of the first boom member around the top end thereof and having a cam face. Said sliding metallic element 46 is also provided with a slidable rod 50 normally urged in the b direction and having a cam face or slot 51 facing a roller 52 provided at the top end of the plunger 40. One end of the rod 50 confronts the base portion of the third boom member 3.

The thus constructed switching valve 33 operates as follows. When the first and second hydraulic cylinders 11, 12 are in the mostly retracted position, the plunger 40 is retained in the position as shown in FIG. 3, namely in the first position I in FIG. 2, in which the oil pressure supply and discharge lines 32 and 34 are communicated with each other while the lines 32 and 35 are cut off. As soon as the second boom member 2 is moved into the utmostly extended position due to extension of cylinder 11 (as fully explained hereinafter), the roller 47 engages the cam face of projection 48 to push the sliding metallic element 46 somewhat in the a direction, thereby to cause the plunger 40 to move in the a direction, whereby the line 32 becomes communicated with both lines 34 and 35. This is the second position II of the valve as shown in FIG. 2. Subsequently, when the third boom member 3 is caused to somewhat extend due to a partial extension of cylinder 12, the rod 50 is moved in the b direction by the action of the spring 49 into the position shown with the dotted line, and the plunger 40 is further urged in the a direction by the rod 50, whereby oil pressure supply and discharge lines 32 and 34 become cut off while the lines 32 and 35 remain communicated with each other. This is the third position III of the valve as seen in FIG. 2. The switching valve 33 is automatically turned to three positions in association with the extending and retracting motions of boom members, as described.

When the second and third boom members 2, 3 are in the mostly retracted position, namely the first and second hydraulic cylinders ll, 12 are in the mostly retracted position, and if the valve 26 for switching the oil pressure is manually operated (rightwardly in FIG. 2) to connect the oil pressure supply and discharge line 32 to the oil pressure source P and connect the oil pressure supply and discharge line 27 pressed to the reservoir or tank T, the oil pressure is supplied only to the compressed oil chamber on the extending side of the first hydraulic cylinder 11, since the switching valve 33 is still retained in the first position I. Therefore, only the first hydraulic cylinder is extended to cause the second boom member 2 to extend. As soon as said second boom member 2 reaches the utmostly extended position, the switching valve 33 is biased into the second position II, thereby to supply the oil pressure to the line 35, through port 37 into the interior of piston rod 12c, and then into the compressed oil chamber 12c on the extending side of the second hydraulic cylinder 12, whereby the third boom member 3 starts extending. When the third boom member 3 is somewhat extended, the switching valve 33 is further biased to the third position III thereby to cause the second hydraulic cylinder 12 to extend until said hydraulic cylinder 12 reaches the extremity of extension. Accordingly, the third boom member 3 is caused to extend to the extremity. While the extending operation of respective hydraulic cylinders is effected, the oil within the compressed oil chambers 11d, 12d on the retracting sides of respective hydraulic cylinders ll, 12 is returned to the tank through the lines 30 and 27.

When all of hydraulic cylinders are in the utmostly extended positions and if the switching valve 26 is manually biased to the other position (leftwardly in FIG. 2) so as to connect the line 27 to the pressure source and connect the line 32 to the tank, the oil pressure is flowed to the compressed oil chambers 11d, 12d on the retracting sides of hydraulic cylinders ll, 12 in the direction of causing the retraction of these hydraulic cylinders. In the situation where the valve 33 is maintained in the third position, however, the first hydraulic cylinder 11 is not retracted yet since the connection of the compressed oil chamber on the extending side of said first hydraulic cylinder 11 with the oil pressure supply and discharge line 34 is cut off to control the oil discharge therefrom, while the compressed oil chamber on the extending side of the second hydraulic cylinder 12 is communicated with the oil pressure supply and discharge line 32 through the line 35, thereby to pennit the oil discharge therefrom, hence the second hydraulic cylinder 12 is permitted to retract. Accordingly, the second hydraulic cylinder 12 only is firstly retracted to cause the third boom member 3 to retract.

As soon as the third boom member 3 reaches the utmostly retracted position, the switching valve 33 is biased to the second position II, and the first hydraulic cylinder 11 starts retracting. When said first hydraulic cylinder is retracted to some extent, the valve 33 is biased to the first position I, hence only the first hydraulic cylinder 11 is retracted until said hydraulic cylinder reaches the utmostly retracted position. Thus, the second boom member 2 is retracted to the extremity of retraction.

In the above embodiment, the extension means is used in the boom consisting of three boom members, and it is the matter of course that the extension means is applicable for the boom consisting of any desired numbers of boom member upward of three. FIG. 4 is a diagrammatical view of the arrangement of oil pressure supply and discharge lines of the extension means where a extension means is embodied in the fourstage boom. In this example, a third hydraulic cylinder 13 and a switching valve 33' controllable in the same manner as said switching valve 33 are additionally provided.

Another example is shown in FIGS. 5 through 8. The extension means of this embodiment is also used for the three-stage boom, and therefore, the principal construction is similar to that of the first embodiment with the exception of the arrangement of oil pressure supply and discharge lines. Numerals 61, 62 and 63 are first, second and third boom members of a cylindrical shape telescopically slidably connected each to other. Numeral 71 is a first hydraulic cylinder disposed between the first and second boom members 61, 62 to extend in the longitudinal direction thereof, said first hydraulic cylinder 71 having a piston rod 71b pivotally connected at 81 at its one end to the base portion of the first boom member 61 and a cylinder portion 71a pivotally connected at 82 at its base portion to the base portion of the second boom member 62 located at the succeeding position with respect to the first boom member 61. Numeral 72 is a second hydraulic cylinder disposed between the second and third boom members 62, 63 to extend in the longitudinal direction and having a piston rod 72b pivotally connected at 83 at its one end to the base portion of the succeeding second boom member 62 and a cylinder portion 77a pivotally connected at 84 at its top end portion to the top portion of the third boom member 63. Numeral 85 is a roller carrying the top end portion of the first hydraulic cylinder 71.

The connection of oil pressure supply and discharge lines or circuits will be described. Numeral 86 is a valve for switching the oil pressure, and 87 is an oil pressure supply and discharge line communicating with compressed oil chambers 71c, 72c on the extending sides of respective hydraulic cylinders, said oil pressure supply and discharge line 87 being communicated with the compressed oil chamber 710 on the extending side of the first hydraulic cylinder 71 through a port 88 provided at the piston rod 71b of the first hydraulic cylinders 71 and said piston rod 7 lb. Said compressed oil chamber 71c is communicated with the compressed oil chamber 72c on the extending side of the second hydraulic cylinder 72 through a port 89 pro vided at the cylinder portion 71a, an oil pressure supply and discharge line 90, and a port 91 provided at the piston rod 72b of the second hydraulic cylinder 72 and the inner part of the piston rod 72b. Thus, the oil pressure is supplied to and discharged from the compressed oil chambers 71c, 72c on the extending sides of respective hydraulic cylinders 71, 72 through said oil pressure supply and discharge line 87. And the oil pressure supply and discharge to and from the compressed oil chambers 71d, 72d on the retracting sides of respective hydraulic cylinders 71, 72 is conducted through the common oil pressure supply and discharge line 92 connected to said switching valve 86 and a valve 93 for switching the oil pressure. Respective compressed oil chambers 71d, 72d on the retracting sides of hydraulic cylinders 71, 72 and said valve for switching the oil pressure are connected through the oil pressure supply and discharge lines 94, 95, respectively. Numeral 96 is a port connecting the line 94 to the compressed oil chamber 71d on the retracting side of the first hydraulic cylinder 71, and numeral 97 is a port provided at the piston rod 72b for connecting the oil pressure supply and discharge circuit 95 to the compressed oil chamber 72d on the retracting side of the second hydraulic cylinder 72, said port 97 being communicated with said compressed oil chamber 72d on the retracting side through an oil passage 72c provided at the piston rod 72b.

Said valve 93 for switching the oil pressure is secured to the second boom member 62 and moved with said second boom member 62, as in the first embodiment. Means for extending the oil pressure supply and discharge line 92 connected to the switching valve 93 has the same construction as in the first embodiment. The switching valve 93 employed in this embodiment is quite the same in structure as the valve 33 of the first embodiment, and therefore, description of its structure is omitted.

When the second and third boom members 62, 63 are in the utmostly retracted position, namely the first and second hydraulic cylinders 71 and 72 are in the mostly retracted position, and if the switching valve 86 is manually operated to connect the oil pressure supply and discharge line 87 to the oil pressure source P and connect the oil pressure supply and discharge line 92 to the tank T, the oil pressure is supplied through line 87 and is applied simultaneously to the compressed oil chambers 71c, 720 (due to the intermediate line on the extending sides of respective hydraulic cylinders 71, 72 to move then in the extending direction. However, the oil discharge is permitted only in the compressed oil chamber 71d on the retracting side of the first hydraulic cylinder 71, since the switching valve 93, in this situation, is retained in the first position I. Accordingly, only the first hydraulic cylinder 71 is firstly extended, hence the second boom member 62 is caused to extend.

As soon as the second boom member 62 is extended to the extremity, the switching valve 93 is biased to the second position I], and the oil discharge from the compressed oil chamber 72c on the retracting side of the second hydraulic cylinder 72 is permitted, whereby the third boom member 63 starts extending. When said third boom member 63 is extended a limited amount, the switching valve 93 is biased to the third position III, and hence the second hydraulic cylinder 72 is extended until it reaches the utmostly extended position, whereby the third boom member 63 is moved to the extremity of extension.

At this time, if the switching valve 86 is manually operated to change the connection of the oil pressure supply and discharge lines 92, 87 with the pressure source and the tank, e.g., to connect the line 92 to the pressure source and to connect the line 87 to the tank, the connection of the oil pressure supply and discharge line 94 with the oil supply line 92 is cut off through the intermediary of the switching valve 93 retained in the third position, while the line communicates only with the oil supply line 92. Hence, since a back pressure is not caused in the compressed oil chamber 71d on the retracting side of the first hydraulic cylinder 71, only the second hydraulic cylinder 72 is retracted to cause the third boom member 63 to retract. When said boom member 63 is retracted to the extremity, said switching valve 93 is biased to the second position by the base portion of said third boom member 63, hence the oil pressure is fed to the compressed oil chamber 71d on the retracting side of the first hydraulic cylinder 71 thereby to cause the first hydraulic cylinder 71 to retract, whereby the second boom member 62 is caused to retract. When the second boom member 62 is retracted to some extent, the switching valve 93 is biased to the first position I thereby to permit the retraction of the first hydraulic cylinder 71 only. Said first hydraulic cylinder 71 is retracted until it reaches the utmostly retracted position, whereby the secured boom member 62 is also retracted to the extremity.

At the time of retraction of respective hydraulic cylinders, the oil within the compressed oil chambers 72c, 710 on the extending sides of respective hydraulic cylinders 72, 71 is returned to the tank through the lines 90, 87.

The extension means of this embodiment is applicable to a boom consisting of any desired numbers of boom member upward of three. FIG. 8 shows the arrangement of oil pressure supply and discharge lines in the extension means which is used with a four-stage boom. In this case, there is additionally provided a third hydraulic cylinder 73 and a valve 93 for switching the oil pressure which is controllable in the same manner as in the above embodiment.

FIG. 9 is a diagrammatical view of another circuit arrangement in the extension means which is similarly used with a four-stage boom. The difference between the example of FIG. 8 and that of FIG. 9 is found in the point that, in the former example, the switching valves 93, 93' are respectively connected to the oil pressure supply and discharge lines communicating with compressed oil chambers on the retracting sides of the succeeding hydraulic cylinders, while in the latter, these valves 93, 93 are respectively connected to the lines communicating with the compressed oil chambers on the retracting sides of the preceding hydraulic cylinders.

It is the matter of course that the valve 33 or 93 for switching the oil pressure, of which the operation is automatically controlled according to the extending and retracting motions of boom members, may be controlled indirectly by a solenoid which operates depending upon the extending and retracting positions of respective hydraulic cylinders.

The extension means of a multi-stage extensible boom relating to the present invention presents such advantages that respective hydraulic cylinders can be automatically and regularly extended and retracted according to the predetermined sequence by the manual operation of a single valve for switching the oil pressure thereby to assure the operational sequence of respective boom members, and hence, the stable condition of extension of the multi-stage boom is usually ensured. The extension means has other advantages in that the arrangement of oil pressure supply and discharge lines is simple and the oil supply and discharge is easily. controlled to assure the operational sequence of hydraulic cylinders.

What is claimed is:

1. In a boom having a plurality of telescopic boom sections and particularly including first and second telescopically interconnected boom sections and first double-acting fluid pressure cylinder means interconnected between and coacting with said first and second boom sections for permitting said second boom section to be telescopically extended or retracted relative to said first boom section, said boom also including a third boom section telescopically associated with said first and second boom sections and second double-acting fluid pressure cylinder means associated with and coacting between said second and third boom sections for permitting said third boom section to be telescopically extended or retracted relative to said second boom section, and a fluid pressure system interconnected to said first and second cylinder means for supplying pressure fluid to said cylinder means to cause extension or retraction of said boom, the improvement comprising:

first and second conduit means respectively connected to said first and second cylinder means for supplying pressure fluid to or discharging pressure fluid from said cylinder means;

third conduit means selectively connectible to a fluid pres sure supply source;

shiftable valve means associated with said first, second and third conduit means for selectively permitting communication between said third conduit means and at least one of said first and second conduit means, said valve means being shiftable between first and second positions for permitting said third conduit means to alternately communicate with said first and second conduit means, respectively; and

actuator means coacting with said valve means for causing shifting of said valve means between said first and second positions in response to relative extension or retraction of said boom sections for causing the boom sections to be automatically but sequentially extended or retracted.

2. A boom according to claim 1, wherein said shiftable valve means is mounted on said second boom section, and said actuator means coacting with one of said first and third boom sections for causing shifting of said valve means when said one boom section is substantially fully extended relative to said second boom section.

3. A boom according to claim 1, wherein said shiftable valve means is normally biased into one of said first and second posi tions for causing one of said second and third boom sections to be initially extended relative to said first boom section, and said actuator means coacting. with said one boom section when it is substantially fully extended for causing shifting of said valve means into the other of said first and second positions to thereby cause the other of said second and third boom sections to be extended.

4. A boom according to claim 3, wherein said shiftable valve means is movable into a third position disposed intermediate said first and second positions, said valve means when in said third position causing said third conduit means to be connected to both said first and second conduit means, and said actuator means including a first actuator member coacting with said one boom section when same is substantially fully extended for causing movement of said valve means from said one position into said third position, and said actuator means including a second actuator member coacting with said other boom section for shifting said valve means from said third position into said other position after said other boom section has been initially extended a small amount.

5. A boom according to claim 4, wherein said shiftable valve means is mounted on said second boom section, and said first and second actuator members both being movably mounted on said second boom section and disposed for coaction with said first and third boom sections, respectively.

6. A boom according to claim 5, wherein said first actuator member is disposed for movement in a direction substantially transverse to the direction of extension of said boom and cam means provided adjacent the free end of said first boom section and disposed for causing movement of said first actuator member to cause said valve means to be shifted from said one position into said third position, and said second actuator member being mounted for movement in a direction substantially parallel to the direction of extension of said boom, said second actuator member being normally resiliently urged into abutting engagement with said third boom section when said second and third boom sections are fully retracted, whereby the resilient urging of said second actuator member causes movement thereof in response to the initial extension of said third boom section relative to said second boom section for causing said valve means to be shifted from said third position into said other position.

7. A boom according to claim 1, wherein said first and second conduit means are respectively connected to the extending sides of said first and second cylinder means, said valve means including biasing means coacting therewith for normally maintaining said valve means in one of said first and second positions whereby only one of said first and second conduit means is interconnected to said third conduit means whereby pressure fluid is supplied to one of said cylinder means for causing relative extension between two of said boom sections, and said actuator means causing said valve means to be shifted to the other of said first and second positions for permitting pressure fluid to be supplied to the other cylinder means only when said one cylinder means reaches its fully extended position.

8. A boom according to claim 7, further including fourth conduit means connected to the retraction side of one of said cylinder means, fifth conduit means connected between the retraction sides of said first and second cylinder means, and a manual control valve means associated with said third and fourth conduit means and manually shiftable between positions permitting pressure fluid to be supplied to either said third conduit means or said fourth conduit means.

9. A boom according to claim 1, wherein said first and second conduit means are respectively connected to the retracting sides of the first and second cylinder means, biasing means for then causing retraction thereof.

10. A boom according to claim 9, further including fourth conduit means communicating with the extending side of one of said cylinder means, and fifth conduit means communicating between the extending sides of said first and second cylinder means, and manual control valve means associated with said third and fourth conduit means and selectively manually shiftable for permitting pressure fluid to be supplied to either said third or said fourth conduit means.

* i i IR 

1. In a boom having a plurality of telescopic boom sections and particularly including first and second telescopically interconnected boom sections and first double-acting fluid pressure cylinder means interconnected between and coacting with said first and second boom sections for permitting said second boom section to be telescopically extended or retracted relative to said first boom section, said boom also including a third boom section telescopically associated with said first and second boom sections and second double-acting fluid pressure cylinder means associated with and coacting between said second and third boom sections for permitting said third boom section to be telescopically extended or retracted relative to said second boom section, and a fluid pressure system interconnected to said first and second cylinder means for supplying pressure fluid to said cylinder means to cause extension or retraction of said boom, the improvement comprising: first and second conduit means respectively connected to said first and second cylinder means for supplying pressure fluid to or discharging pressure fluid from said cylinder means; third conduit means selectively connectible to a fluid pressure supply source; shiftable valve means associated with said first, second and third conduit means for selectively permitting communication between said third conduit means and at least one of said first and second conduit means, said valve means being shiftable between first and second positions for permitting said third conduit means to alternately communicate with said first and second conduit means, respectively; and actuator means coacting with said valve means for causing shifting of said valve means between said first and second positions in response to relative extension or retraction of said boom sections for causing the boom sections to be automatically but sequentially extended or retracted.
 2. A boom according to claim 1, wherein said shiftable valve means is mounted on said second boom section, and said actuator means coacting with one of said first and third boom sections for causing shifting of said valve means when said one boom section is substantially fully extended relative to said second boom section.
 3. A boom according to claim 1, wherein said shiftable valve means is normally biased into one of said first and second positions for causing one of said second and third boom sections to be initially extended relative to said first boom section, and said actuator means coacting with said one boom section when it is substantially fully extended for causing shifting of said valve means into the other of said first and second positions to thereby cause the other of said second and third boom sections to be extended.
 4. A boom according to claim 3, wherein said shiftable valve means is movable into a third position disposed intermediate said first and second positions, said valve means when in said third position causing said third conduit means to be connected to both said first and second conduit means, and said actuator means including a first actuator member coacting with said one boom section when same is substantially fully extended for causing movement of said valve means from said one position into said third position, and said actuator means including a second actuator member coacting with said other boom section for shifting said valve means from said third position into said other position after said other boom section has been initially extended a small amount.
 5. A boom according to claim 4, wherein said shiftable valve means is mounted on said second boom section, and said first and second actuator members both being movably mounted on said second boom section and disposed for coaction with said first and third boom sections, respectively.
 6. A boom according to claim 5, wherein said first actuator member is disposed for movement in a direction substantially transverse to the direction of extension of said boom and cam means provided adjacent the free end of said first boom section and disposed for causing movement of said first actuator member to cause said valve means to be shifted from said one position into said third position, and said second actuator member being mounted for movement in a direction substantially parallel to the direction of extension of said boom, said second actuator member being normally resiliently urged into abutting engagement with said third boom section when said second and third boom sections are fully retracted, whereby the resilient urging of said second actuator member causes movement thereof in response to the initial extension of said third boom section relative to said second boom section for causing said valve means to be shifted from said third position into said other position.
 7. A boom according to claim 1, wherein said first and second conduit means are respectively connected to the extending sides of said first and second cylinder means, said valve means including biasing means coacting therewith for normally maintaining said valve means in one of said first and second positions whereby only one of said first and second conduit means is interconnected to said third conduit means whereby pressure fluid is supplied to one of said cylinder means for causing relative extension between two of said boom sections, and said actuator means causing said valve means to be shifted to the other of said first and second positions for permitting pressure fluid to be supplied to the other cylinder means only when said one cylinder means reaches its fully extended position.
 8. A boom according to claim 7, further including fourth conduit means connected to the retraction side of one of said cylinder means, fifth conduit means connected between the retraction sides of said first and second cylinder means, and a manual control valve means associated with said third and fourth conduit means and manually shiftable between positions permitting pressure fluid to be supplied to either said third conduit means or said fourth conduit means.
 9. A boom according to claim 1, wherein said first and second conduit means are respectively connected to the retracting sides of the first and second cylinder means, biasing means coacting With said switching valve means for normally maintaining same in one of said first and second positions whereby only one of said first and second conduit means is normally disposed in communication with said third conduit means, said actuator means causing said switching valve means to be moved to the other of said first and second positions only when said one cylinder means reaches its substantially fully retracted position while said other cylinder means is substantially in its fully extended position, whereby said third conduit means thus communicates with said other cylinder means for then causing retraction thereof.
 10. A boom according to claim 9, further including fourth conduit means communicating with the extending side of one of said cylinder means, and fifth conduit means communicating between the extending sides of said first and second cylinder means, and manual control valve means associated with said third and fourth conduit means and selectively manually shiftable for permitting pressure fluid to be supplied to either said third or said fourth conduit means. 